Nondestructive testing techniques to evaluate the structural damage of historical city walls

In the current study, the structural damage that took place on the historical Diyarbakir City Walls province was investigated by performing nondestructive testing methods. This province has been included in the UNESCO Cultural Heritage List thanks to its city walls and Hevsel Gardens. The city walls in the Diyarbakir was built by masonry construction technique with using basalt stone like many other structures available in the city such as churches, mosques, guard towers, madrasahs, inns, etc. The Diyarbakir province has been home to many civilizations, cultures, and religions. Therefore, the traces from many different civilizations, cultures, and religions can be observed inside the city walls. Since the Diyarbakir City Walls were included in the UNESCO Cultural Heritage List, any investigation going to be conducting on the city walls should be either by observational methods or by nondestructive testing (NDT) techniques. For this reason, the determination of the structural performance of city walls was done by carrying out the NDT techniques such as crack opening, ultrasonic velocity and time, levelness, temperature-humidity measurement, and ground penetration radar tests. Monthly changes over the 1-year period were measured from the different places of Urfa Gate, which is one of four main gates of the city walls. The results indicated that both ultrasonic velocity and time were influenced by seasonal changes. The basalt stones having the cracks require to be urgently renewed since it was observed decreasing in the ultrasonic pulse velocity of the basalt stone. Nevertheless, no remarkable effect of temperature on the integrity of the city walls and no significant effect of seasonal changes on levelness were observed. Besides, it was noticed that the highest crack opening values were measured in the autumn season while the lowest values were measured during the summer months. In addition to all, the radar images verified that on the foundation and ground there were no settlements and damages. (C) 2020 Elsevier Ltd. All rights reserved.